1. Field of the Invention
The present invention relates to an optical device such as an optical multiplexer/demultiplexer, an optical isolator, an optical circulator, an optical switch, and an optical gain equalizer, a lens assembly for use in the optical device, and an optical axis adjusting method for the optical device.
2. Description of the Related Art
In an optical device of this type, normally, in an accommodation sleeve of a cylindrical shape, a lens assembly in which two lenses are fixed by an adhesive or the like so as to be opposed to each other through an intermediation of an optical functional component (such as optical filter or optical isolator core) is incorporated. There is known an optical device in which a capillary tube to which an end portion of an optical fiber is fixed is fixed by an adhesive or the like while being inserted into the accommodation sleeve of the lens assembly (for example, Patent Document 1 mentioned below). The lens has a function of making light emitted from the optical fiber parallel and of collecting the parallel light to allow the collected light to incident onto the optical fiber. As the lens, there is used a cylindrical shape lens of a gradient index type (so-called GRIN lens: one end thereof is set to be vertical surface perpendicular to optical axis, and another end thereof is set to be inclined surface in many cases), a cylindrical shape lens having a uniform refractive index, in which two partial spherical lens surfaces having the same center of curvature as each other are provided on both ends (so-called drum lens), a cylindrical shape lens having the uniform refractive index, in which the partial spherical lens surface is provided on one end (so-called C lens: another end thereof is set to be inclined surface in many cases), an aspherical lens, or the like.
Further, as the optical device of this type, there are commonly known the optical device in which a pair of lens capillary tube assemblies are manufactured, in each of which a capillary tube, to which an end portion of an optical fiber is fixed, and a lens are fixed by an adhesive to a common sleeve, and the pair of lens capillary tube assemblies are fixed by the adhesive to an inner portion of an accommodation member (cylindrical member or box member) such that the lenses are opposed to each other through an intermediation of an optical functional component (for example, Patent Documents 1 to 4 mentioned below).
Each of the lenses of the pair of lens capillary tube assemblies has a function of collimating light emitted from the optical fiber into parallel light and of collecting the parallel light to allow the collected light to be incident on the optical fiber. As the lens, there is used a cylindrical shape lens of a gradient refractive index type, which is called a GRIN lens, a cylindrical shape lens having a uniform refractive index, which is called a drum lens, a cylindrical shape lens having the uniform refractive index, which is called a C lens, an aspherical lens, or the like.
According to Patent Document 5 mentioned below, there is disclosed an optical device including a pair of lens capillary tube assemblies in each of which a capillary tube having two optical fibers are inserted thereinto and fixed thereto is inserted into an inner hole of a retaining sleeve, and a lens is inserted and fixed in a position on a leading end side with respect to the capillary tube in the inner hole of the retaining sleeve, with the pair of lens capillary tube assemblies being fixed to an inner portion of an accommodation member such that the lenses are opposed to each other through an intermediation of an optical functional component (filter).
Further, according to Patent Document 6 mentioned below, there is disclosed an optical multiplexer/demultiplexer for demultiplexing multiplexed light having two wavelengths passing through one optical fiber to two optical fibers, or multiplexing single light beams having different wavelengths separately passing through the two optical fibers, respectively, to one optical fiber. The optical multiplexer/demultiplexer has a structure including a pair of lens capillary tube assemblies in each of which a quadruple-core capillary tube having four optical fibers inserted therein and fixed thereto and a lens (GRIN rod lens) abutted on a leading end of the quadruple-core capillary tube are inserted into an inner hole of a first alignment sleeve, the pair of lens capillary tube assemblies being fixed to each other such that the lenses are opposed to each other through an intermediation of an optical functional component (glass plate having a surface applied with mirror coating). In this case, the pair of lens capillary tube assemblies are fixed to each other by inserting both the lenses into an inner hole of the second alignment sleeve (accommodation member). One of the lens capillary tube assemblies uses two optical fibers of the four optical fibers, which are positioned on a diagonal line in a plane perpendicular to an axis, and another of the lens capillary tube assemblies uses only one of the four optical fibers, thereby making it possible to align both the lens capillary tube assemblies without being decentered.
Further, in Patent Document 7 mentioned below, in order to enable optical axis adjustment between an optical fiber and a lens, a capillary tube assembly in which a capillary tube (ferrule) to which an end portion of the optical fiber is fixed is embedded in a recessed portion of a sleeve and a lens assembly in which a lens is fixed to an inside of a cylindrical bush are manufactured, relative positions of the capillary tube assembly and the lens assembly are adjusted, to thereby perform optical axis adjustment between the optical fiber and the lens, and then an end surface of the sleeve and an end surface of the cylindrical bush are fixed to each other. In this case, a leading end surface of the optical fiber and an end surface of the capillary tube retaining the optical fiber is polished to form a spherical shape and the capillary tube is pressed by the sleeve, thereby allowing the leading end surface of the optical fiber to be brought into PC contact (physical contact) with an incident/emission surface of the lens. As the lens, the GRIN lens is used and a filter serving as the optical functional component is fixed to a member (base member 7b) separate from the lens assembly to be interposed between lens assemblies which are opposed to each other.    [Patent Document 1] JP 2002-182061 A    [Patent Document 2] JP 2003-344697 A    [Patent Document 3] JP 2005-10372 A    [Patent Document 4] JP 2005-24928 A    [Patent Document 5] JP 3135511 B    [Patent Document 6] JP 3124467 B    [Patent Document 7] JP 2004-271894 A